1. Field of the Invention
The invention relates to a semiconductor light-emitting device with enhanced light-extraction efficiency.
2. Description of the Related Art
A conventional semiconductor light-emitting device (e.g., see JP-A-2005-513787) with improved light-extraction efficiency is known that is composed of a conductive holder, a semiconductor multilayer structure having multiple semiconductor layers including a light-emitting layer, a reflection layer of a metal and plural interface electrodes and formed on the conductive holder through a transparent layer having a thickness d of λ/(4n), and a surface electrode formed on the semiconductor multilayer structure, where the interface electrodes are formed in an area except under the surface electrode. Meanwhile, λ represents a wavelength of light emitted from the light-emitting layer, and n is a refractive index of the transparent layer.
A refractive index of the semiconductor layer composing the semiconductor light-emitting device is greater than that of the transparent layer of a dielectric material so that, of light inputted to the interface between the semiconductor layer and the transparent layer, light at an incident angle greater than a total reflection critical angle cannot be externally discharged from the device.
Here, in considering only light inputted perpendicularly to the interface between the semiconductor layer and the transparent layer, the reflectivity a reflection region becomes maximum when a thickness d of the transparent layer is d=λ/(4 n), where the reflection region is formed by sandwiching the transparent layer with a lower refractive index than that of the semiconductor layer composing the semiconductor multilayer structure, between the reflection layer and the semiconductor multilayer structure as in the semiconductor light-emitting device of JP-A-2005-513787.
The semiconductor light-emitting device of JP-A-2005-513787 functions such that light emitted from the light-emitting layer can be reflected by the reflection layer outside the device, and owing to the thickness of the transparent layer defined as d=λ/(4 n), its reflection characteristic can be enhanced with respect to light inputted perpendicularly to the reflection region composed of the transparent layer and the metal layer, whereby the light-extraction efficiency can be enhanced. Furthermore, the semiconductor light-emitting device can be enhanced in light-extraction efficiency due to having the roughened surface of the semiconductor multilayer structure.
However, in the semiconductor light-emitting device of JP-A-2005-513787, the thickness of the transparent layer is optimized only with respect to light inputted perpendicularly to the reflection region. In other words, no optimization is considered with respect to a light component inputted obliquely to the reflection region. Therefore, in the semiconductor light-emitting device of JP-A-2005-513787, light inputted obliquely to the reflection region may be reflected repeatedly in the reflection region to reduce the intensity. Thus, of light emitted from the light-emitting layer, light inputted obliquely to the reflection region is difficult to efficiently extract from the semiconductor light-emitting device.